The present invention relates to a method and apparatus for the cutting of a fibrous tubular product, and more specifically, to the longitudinal cutting of the wall of a fibrous tubular product in a step-shaped profile.
The fibrous tubular product is a hollow cylinder formed of fibers, such as, for example, glass fibers, held together by a polymerized binder. The tubular product is formed by impregnating a mat of fibers with a sizing composition, wrapping the impregnated fibers around a heated mandrel to form a tube or shell, and polymerizing the sizing in a polymerization oven. Such a product typically is used for insulation of conduits. A longitudinal cut along the shell to open and close the shell is necessary to place the shell around conduit. However, a single radial cut along the shell can give rise to undesirable heat losses.
A process is known where insulating shells are cut to obtain a step shaped profile so that the walls, when closed around the conduit, overlap at the step, thus limiting heat loss. According to this known process, two substantially parallel cuts are made into the shell wall from opposite sides of the wall. These two cuts are displaced slightly and only partially extend into the shell wall. To obtain a complete cut through the shell wall, shearing forces are applied near the edges of the slits within the wall. These forces act on the material between the parallel slits and tend to tear it.
Such a process has the disadvantage of inducing mechanical stresses in the fibrous product. These stresses can weaken and disintegrate the fibrous structure and result in irregular cut profiles leading to incomplete closing and therefore excessive heat loss.